A cellular network is a radio network made up of a number of radio cells each served by a transceiver, known as a cell site or base station. Cellular networks are inherently asymmetric such that a set of fixed transceivers serve a cell and a set of distributed mobile transceivers provide services to the users.
A cellular network is able to provide more transmission capacity than a single transmitter network because a radio frequency of a cell can be reused in another cell for different transmission. Frequency reuse, however, causes interference between cells that use the same and nearby frequencies.
This inter-cell interference has conventionally been solved by coordination/planning based methods. An example of such methods is frequency reuse where different groups of radio channels may be assigned to adjacent cells, and the same groups are assigned to cells separated by a certain distance (reuse distance) to reduce co-channel interference. The method is relatively effective and straightforward, but wastes channel resource.
Another alternative is provided by co-ordination/planning based methods that comprise use of dynamic channels temporarily assigned for use in cells for the duration of the call, returned and kept in a central pool after the call is over. In some other dynamic solutions the total number of channels is divided into two groups, one of which is used for fixed allocation to the cells, while the other is kept as a central poor to be shared by all users. The reuse factor of these methods still remains low, actually in heavy traffic load they may perform worse than the above disclosed fixed channel assignment method.
In the new emerging systems, for example in the upcoming evolution of 3rd Generation Partnership Project (3GPP) systems (also called as Long Term Evolution (LTE) systems), the requirements, according to the working assumptions, are challenging. The planned frequency reuse factor is 1, and at the same time significantly improved system performance, in terms or average throughput and cell throughput is targeted. In order to meet these challenges, mitigation of inter-cell interference is now extensively studied.
The approaches considered in inter-cell interference mitigation comprise Inter-cell-interference co-ordination/avoidance. The common theme of inter-cell-interference co-ordination/avoidance is to apply restrictions to the resource management (configuration for the common channels and scheduling for the non common channels) in a coordinated way between cells. Such restrictions in a cell will provide the possibility for improvement in (Signal-to-Interference Ratio) SIR, and cell-edge data-rates/coverage, on the corresponding time/frequency resources in a neighbor cell.
The available inter-cell interference co-ordination methods require certain inter-communication between different network nodes in order to set and reconfigure the above mentioned restrictions. However, links between cells are expensive and typically cause delays. Thus, for the time being it seems that reconfiguration of the restrictions will be done on a time scale corresponding to days, and the inter-node communication is going to be very limited, basically with a rate of in the order of days. In such scenarios mechanisms that do not rely on inter-cell co-ordination are critically needed.